WarmGlass.com

We have been building a new house (yes, a new workshop!!!) so my kiln has been in storage for 8 months. I cleaned my shelf and put on new kiln wash (we have moved in) and fired four times. Last nite, I fired a single layer with powder designs (as I have done 4 times this week) and I have a huge bubble in the one last nite. Sked: 600dph to 1350, hold 10, afap to 900 hold 30 and natural cooling. I believe my shelf is warped as it sinks at least enough to put a piece of paper under a level(straight edge). Turned it over and it sinks in the middle on that side too, although not as much. What happened? Of course it's Sunday and no place to order or purchase a new shelf, and I thought I was going to get over my "glass withdrawal" and now I'm not!!!

Pat@aslowfuse.com

My guess is the one layer. There is not enough glass to resist a small amount of trapped air. Sometimes you can get lucky but as a general rule a single layer is going to blow a bubble.

Jim